Field of the Invention
Example embodiments relate generally to nuclear Boiling Water Reactors (BWRs), and more particularly to a system and a method for injecting hydrogen into reactor support systems during periods of reactor startup and shutdown. The system is capable of providing hydrogen at variable pressures (including high pressures of about 1,100 psig) in order to match the changing operating pressures of the support systems throughout the startup and shutdown modes.
Related Art
Conventionally, Hydrogen Water Chemistry (HWC) systems 1 (see FIG. 1) inject hydrogen into feedwater systems at the suction of the condensate booster pumps or at the suction of the feedwater pumps (see injection point 2) of a Boiling Water Reactor (BWR). Injection of hydrogen into these locations helps mitigate Inter-Granular Stress Corrosion Cracking (IGSCC) in the recirculation piping and reactor internals. Specifically, the injected hydrogen causes a reduction in dissolved oxygen by lowering the radiolytic net production of hydrogen and oxygen in the core region of the reactor.
The conventional HWC system 1 includes a hydrogen source 4 which may be a liquid storage tank (with compressors and vaporizers) or bottles of hydrogen. The hydrogen source may also be electrolytically generated. A hydrogen filter 6 may filter the hydrogen prior to the hydrogen passing through a series of valves, which may include a pressure control valve 8, excess flow check valve 11, shutoff valves 10 and bypass valves 12. An air-operated control valve 14 may be used to isolate the hydrogen before entering a hydrogen injection module 16 that discharges hydrogen to conventional hydrogen injection points 2. Purge connections 70 throughout the system 1 are generally used for maintenance and safety purposes.
The conventional hydrogen injection points 2 are injection points located in lower-pressure systems (relative to the reactor), such as the suctions of the condensate booster pumps (85-160 psig) and the suctions of the feedwater pumps (400-650 psig). Because the pumps of these lower-pressure systems are not in service during the full reactor startup or shutdown (including emergency reactor shutdown, such as a reactor SCRAM), hydrogen therefore may not be injected at these conventional locations during startup and shutdown, as doing so would not allow hydrogen dissolution for efficient transport to the recirculation piping and/or reactor internals. Because IGSCC corrosion is more prevalent at lower operating temperatures (of about 200° F. to about 450° F., during reactor startup/heat-up to about 5% power), the reactor (and the reactor support systems) is at greater risk during startup and shutdown modes, thereby exacerbating the effects that are caused by an inability to inject hydrogen into the conventional injection points 2 during reactor startup and shutdown modes.